With opponents and supporters packing the galleries overlooking the floor of the chamber, the House of Delegates gave preliminary approval by voice vote on Tuesday to an omnibus gun control bill proposed by the governor.

After nearly six hours of debate and more than 20 proposed amendments, the House advanced the bill, which would ban certain assault-style guns; limit the maximum number of rounds in magazines to 10; require fingerprints, training and a $50 fee from those seeking a license for a regulated firearm; allow the Maryland State Police to audit gun dealers; and require owners of regulated firearms to report within 72 hours when their guns are lost or stolen.

Gov. Martin O’Malley (D) introduced the far-reaching bill in the early days of the session. Hearings and debates have brought some of the biggest crowds of the 2013 session.

The proposal also has a mental health component, banning individuals previously involuntarily committed to a mental health facility, found incompetent to stand trial or under legal guardianship due to mental or fiduciary reasons from owning firearms.

Current owners of what would be banned assault weapons under the bill would have their firearms grandfathered in, as would anyone who places a verifiable order between now and Oct. 1, when the bill would go into affect.

“The strongest piece really is the licensing part,” said Del. Kathleen M. Dumais (D-Dist. 15) of Rockville, who led debate on the floor. “I think that’s what’s going to do the most good for the state of Maryland.”

During debate, the training requirement in the bill was altered, refocusing on safe handling of a firearm, rather than the proficiency requirement that was initially written into the bill. Critics of the original provision said the state lacks the number of gun ranges to accommodate the number of people who would want to be eligible to own a regulated firearm.

Among the amendments offered by Republicans on the floor were those to allow exemptions to the assault rifle ban for competition shooting events, to strike the licensing and fingerprinting provisions and to require the governor to include money in the budget to run a public information campaign about seeking mental health treatment.

Another proposed amendment was to strike the AR-15 rifle from the banned assault weapons list.

“It is not an assault rifle. It is just a semi-automatic gun,” said Del. Kathryn L. Afzali (R-Dist. 4A) of Middletown, who introduced the amendment. She said the AR-15 is an important gun for women, because it is light and easy to handle. “Another thing that’s important about this gun is that it looks scary,” Afzali added, noting that she and other women would want to look intimidating in the event of a home intruder.

Another amendment offered, and subsequently defeated, was a familiar one.

During the House joint committee debate, an amendment was proposed that would eliminate diminution credits for those who are convicted of using a gun to commit a crime of violence, meaning they would not be eligible to reduce their incarceration time through good behavior. The amendment initially passed in the committee, but leadership called for a re-vote and it was defeated 23-23.

“If you look through this bill there is not one line, one word, about punishing bad men with guns,” Del. Michael D. Smigiel Sr. (R-Dist. 36) of Chesapeake City said.

A similar amendment also was defeated in the Senate committee.

Critics of the measure said that it would cost too much to keep gun offenders in prison, and eliminate the incentive for good behavior from inmates.

The bill still will need a final vote from the House, which could come as soon as Wednesday. It will need to go to a conference committee, as the version the House passes looks to have significant differences from that of the Senate.